The first section in this chapter explains the concept of “kinds” in Fortran. The second section presents several guidelines for using floating-point numbers in the context of performing numerical calculations using a representation that is by nature inexact. The third section presents some aspects of the floating-point exception handling that are now part of modern Fortran. Finally, in the fourth section we present some of the bit manipulation features.

The Concept of KIND

Modern Fortran characterizes the sizes and characteristics of integers, floating-point numbers and other data types as different kinds, and parameterizes them by kind type parameter values. For example, the Fortran processor will almost certainly provide a kind type parameter that corresponds to a four byte real. For one Fortran processor, the kind type parameter value may be 4, corresponding to the number of bytes; but, for a second processor, it could be 1, corresponding to the lowest precision available. The processor may also provide kind type parameters that correspond to single-byte, two-byte, and eight-byte integers.

The standard requires the processor provide at least one integer type. Similarly, two real kinds must be available. The default real kind is the less precise of the two. Normally, the default real will correspond to “single precision,” and the additional required kind to “double precision.” Thus, a processor may support several sizes of integers, each with a different kind type parameter value, and likewise for reals.